Alright let me first say i have never done any structure work to a house besides putting up vinyl siding…, that is why i am asking you all this to better inform me on the steps i should take. I recently bought a house 3 or 4 months ago with a detached garage that is pretty much my shop. It measures 20×30 with a half bath. The shop and the house was built new 4 years ago. The walls are made of cinder blocks. The previous owner did not have insulation put up. In fact there is nothing up just the walls and the rafters on the ceiling. My question is if i were to try and insulate this shop what are the steps i should take? I dotn want an insane amount of insulation just enough to keep it bearable during the summer and winter. (i live in Ga, its 110 today). Ive been doing some research and it seems like i would need to put Rigid foam insulation against the walls and then frame in the walls with 2×4’s and dry wall? And when i was watching a show on DIY the other night they put the rigid foam, framed in with 2×4’s and then put roll insulation between the studs, and then drywalled it in. Any help is appreciated. Bear with me!

Skip the spray foam, its not very effieceint, which is why you dont see nearly as much of it the farther north you go. Probably the best bang for your buck, use fiberglass. You want ot make sure you put a moisture barrier on both sides of the insulation, once between teh cinder blocks and the wall, and one between teh wall and the sheetrock. Most insulation is made to fit snugly between two studs so I dont think you need to staple it, just make sure you snug it up to the top before sealing it between the moisture barriers.

Either of the two options would work. I would definately put up 2×4’s at least every 2’ along the walls with a top and bottom plate, make sure your bottom plate (the 2×4 on the bottom of the wall laying flat on the slab) is a treated board.

I don’t really see a need for the rigid insulation. I would just build walls inside of the block walls. Build them on the floor and then stand them up and nail the top plate to the trusses and put some hard nails (concrete nails) through your treated bottom plate into your slab.

As for insulation, they make fiberglass roll insulation to fit inside of walls with studs on 16” centers and 24” centers. Pick witchever spacing you decide and staple it up. You MUST staple it up or it will certainly settle down to the bottom 3rd of the wall and not do much good. The insulation is made to fit snug between the studs, but that will not keep it from falling.

If you are not sure about 16” on center or the 24” on center studs, it doesn’t really matter in your situation. When you have a load bearing wall, you need your studs on 16” centers. If they aren’t load bearing it isn’t mandatory to use 16” centers.

For a shop, I would suggest putting up some 1/2” or 5/8” project plywood rather than the sheetrock. You will be knocking holes in the sheetrock in no time. Plus you can hang some things on plywood walls without finding a stud.

This …. like woodworking … is an area where I have more “book knowledge” than real knowledge, but … one thing to consider … is that you can use 2x6 studs, and get 50% more insulation in there (may or my not equate to 50% higher R-Value. Didn’t check).

If you live in a pretty harsh climate, it might make a big difference for not a WHOLE heap more money.

One thing I haven’t seen covered, is the fact that you don’t need 2×4 walls on the inside. The reason I say this is your statement that you don’t need that much insulation. Let me explain further. In Florida we use 3/4 rigid insulation directly against the block, then nail 1×4 PT verticals over this. Top and bottom 1×4s are preferable, but not necessary. Some cheaper builders use 1×2 furring strips instead. Drywall is hung on the furring giving a dead air space between them. You won’t get a lot of R value, but you will save money. Remember, in Fla. we only have to deal with the heat, and most of that comes through the roof.

One thing we haven’t discussed is your roof/ceiling. If 4 years ago the builder did not use the foil backed sheathing, you can get this sprayed on by most any insulation company. Since its 110 degrees there you’ll really appreciate this reflective spray on stuff. It reduces the amount of heat transferred into the building. When I built my workshop in Austin, the price for the foil backed 1/2 inch OSB wasn’t that much more then regular plywood, so I went and installed that. I was amazed at the difference that makes on how hot it gets inside the building. You can also buy rolls of this foil stuff and staple it to the rafters.

I too suggest using 1/2 plywood for your walls, you’ll thank yourself for doing it many times over when you go to installing shelves and such. If you are in an area that “MIGHT” flood, you should consider drilling holes near the bottom of the plywood to allow any water to quickly drain from behind the walls in the event of flooding.

Check with you local Building & Safety people for their recommended levels of insulation for your area. Probably R29 insulation in the rafters, if you can get it in there. If you have a ceiling, you can have it blown in. This will block off most of the heat. Foam insulation has a higher r-value that fiberglass, and costs more. But it doesn’t have the water issues you would see with ‘glass- it doesn’t soak it up. If you have a metal roof, you can staple radiant barrier film to the bottoms of the rafters, if you have a ridge vent. That would help, if you don’t want to lay in fiberglass. There are new insulation products out there, one which is in a plastic bag when you put it up (I think it’s fiberglass, but I’m not sure). This avoids the itch, and also provides a moisture barrier.

I also live in Georgia. I recently did a basement remodel that had cinder block walls. I waterproofed the walls, framed with 2×4s, installed fiberglass insulation, and nailed up drywall. Actually, I did stone veneer on one wall and drywall on the other three. With our humidity, and if you air condition the shop, you will need some form of moisture protection, or you’ll end up with a nasty mold problem down the road.

Don’t mess with the spray foam. It’s messy and I question its insulation properties. It’s good for hard to reach or oddball shaped areas.

”Typically if you have a conditioned space and you are getting moisture/mold then the unit is over sized for the square footage.”

Very true.

To explain a bit more … people who want “a REALLY BIG a/c unit” ... don’t understand: if it has “too many BTUs” cooling capacity for the space (and all the factors that drive heating and cooling calcs), then it will cycle TOO INFREQUENTLY, giving the unit NO time to remove the humidity from the air.

Good info about framing out a basement, and vapor barriers, in the SE, can be found here.